refactor(mtproto): sync redesign RPC replay ownership

internal/mtprotoedge/rpc_capacity_error.go

@@ -0,0 +1,20 @@
+package mtprotoedge
+
+import "github.com/iamxvbaba/td/mt"
+
+const (
+	rpcWorkerBusyErrorCode    = 500
+	rpcWorkerBusyErrorMessage = "WORKER_BUSY_TOO_LONG_RETRY"
+)
+
+// rpcWorkerBusyError reports transient server admission pressure. A local
+// worker/queue/ledger ceiling is not Telegram flood control: returning a 420
+// FLOOD_WAIT would falsely blame the account and makes clients surface or cache
+// a rate-limit state. Official clients classify 5xx as transient; TDLib and
+// DrKlo additionally recognize WORKER_BUSY_TOO_LONG_RETRY and retry with delay.
+func rpcWorkerBusyError() *mt.RPCError {
+	return &mt.RPCError{
+		ErrorCode:    rpcWorkerBusyErrorCode,
+		ErrorMessage: rpcWorkerBusyErrorMessage,
+	}
+}